Method of making a polyurethane non-pneumatic tire

ABSTRACT

A non-pneumatic tire is disclosed having a polyether polyol urethane elastomeric body with a plurality of angular radial ribs interconnected by webbing. The urethane is formed of at least two isocyanate-end capped polyether polyols of differing molecular weights to yield a tire with improved highway life and good vehicle ride characteristics.

This is a divisional of application Ser. No. 172,038 filed Mar. 23,1988, issued as a U.S. Pat. No. 4,934,425 June 19, 1990.

BACKGROUND OF THE INVENTION

This invention relates to non-pneumatic tires having angularly orientedribbed members and webs between ribs composed of resilient polyetherurethane elastomeric materials. In particular, a urethane made ofpolyether polyols having two distinctly different molecular weights areused to make the urethane elastomer.

Urethanes have been used in the manufacture of solid tires useful forsuch applications as industrial tires, off-the-road tires, bicyclestires and the like. They have not been entirely satisfactory in suchapplications because such urethane solid tires do not have the propercushioning and handling characteristics for a soft vehicle ride on suchapplications as passenger vehicles. Also, such solid tires suffer frominternal heat build-up and subsequent degradation of the elastomermaterial in prolonged high speed service conditions or under roughterrain situations where the tire is being deformed.

Various polyurethane elastomers have been proposed for use on such solidtires, including those described in U.S. Pat. No. 3,798,200 and U.S.Pat. No. 3,963,681 both to Kaneko et al. In these two pieces of priorart it is proposed that polyether urethane elastomers can be utilizedwhich are prepared from two prepolymers having differing molecularweights. In U.S. Pat. No. 3,963,681 it is disclosed that by using a flexlife test such De Mattia it is determined that the preferred urethaneelastomer is one prepared using a polyfunctional isocyanate and apolyether prepared using prepolymers having different average molecularweights. It is further disclosed that for polytetramethylene etherglycol the critical molecular weight is 4,500. One of the two polyethersused to make the invention must have a molecular weight above the 4,500critical molecular weight and the other must be below this criticalmolecular weight in order to achieve the improved De Mattia flex life.U.S. Pat. No. 3,798,200 discloses a 4,000 critical molecular weight forpolytetramethylene glycol ethers utilized in the urethane teaches thatthe average weight of the two polyethers must lie between 4,500 and20,000 weight average molecular weight. It further teaches that one ofthe polyethers must lie below the critical molecular weight of 4,500 andthe other be above such a critical molecular weight. In comparativeExample 9, a composition outside of the invention of the reference isdescribed in which a 1,900 molecular weight polyether and an 850molecular weight is blended 50:50, reacted with 2 mols of 2,4 tolylenediisocyanate and subsequently cured with methylene bisortho-chloroaniline. Such a composition was found to have poor cutgrowth and flex crack resistance as measured by De Mattia flex testing.

Contrary to the teachings of U.S. Pat. No. 3,798,200, it has been quiteunexpectedly found that a non-pneumatic tire utilizing a rib-and-webstructure of this invention yields a non-pneumatic tire which canfavorably compare with pneumatic tires for service life under both highspeed, long duration test conditions and under very rough roadconditions while still giving good ride and handling characteristicssimilar to a pneumatic tire. Such a device of the invention is superiorto a pneumatic tire in that it cannot be punctured or damaged in the waya pneumatic can.

The non-pneumatic tire concept set forward in European patentpublication number 159,888 which claimed convention priority from U.S.application Ser. No. 600,932 filed Apr. 16, 1984, introduced aconfiguration of tire which utilized an entirely new design approach toa high speed non-pneumatic tire having suitable ride characteristics forpassenger tires. This design features the ability of the ribs and websto provide a variable spring rate in the tires and enables it to deformlocally when an obstacle is encountered on a rough road drivingcondition. These requirements are in addition to the common requirementswhich were encountered in previous generations of solid tires that theinternal heat build-up be kept to a minimum and the flex life of thetire be long.

In view of the unique requirements of structure as a object of theinvention to provide a urethane material which can endure both longduration, high speed conditions as well as the ability to locallydeflect in rough terrain service. It is a further object to provide anon-pneumatic tire having good vehicle ride characteristics under avariety of road conditions. In order to achieve such results, it isnecessary to recognize that dynamic modulus of the material iscritically important as well as flex fatigue life and dynamic heatbuild-up properties (hysteresis). The recognition of the criticality ofutilizing a urethane with two distinct molecular weight glycols with anorganic diamine curative provided the balance in properties required forgood vehicle ride characteristics as well as long life.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one embodiment of the invention there is provided: anon-pneumatic tire rotatable about an axis, having improved hysteresisand flex fatigue resistance comprising: an annular body of resilientpolyether urethane elastomeric material formed of a first isocyanate endcapped low molecular weight polyether polyol having a molecular weightof between 200 and 1,500 and a second high molecular weight isocyanateend capped polyether polyol having a molecular weight between 1,500 and4,000 cured with an aromatic diamine curative, said annular body havinga generally cylindrical outer member at the outer periphery thereof, agenerally cylindrical inner member spaced radially inward from andcoaxial with said outer member, a plurality of axially extending,circumferentially spaced-apart rib members connected at theircorresponding inner and outer ends to said inner and outer cylindricalmembers, said rib members being generally inclined at an angle of about0° to 75° to radial planes which intersect them at their inner ends, andat least one web member having opposite side faces, said web memberhaving its inner and outer peripheries connected respectively to saidinner and outer cylindrical members, said web member being connected onat least one of its side faces to at least one of said rib members tothereby form with said rib member a load-carrying structure for saidouter cylindrical member, said load carrying structure being constructedto permit locally loaded members to buckle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side elevation view of a non-pneumatic tire and rim assemblyembodying the invention;

FIG. 2 is an enlarged fragmentary view of a portion of the tire and rimassembly shown in FIG. 1, showing the intermediate load-carrying andcushioning structure thereof in greater detail: and

FIG. 3 is a sectional elevation view, taken along the line 3--3 of FIG.2, showing one single-web member version of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1, 2 and 3 wherein a preferred embodiment of thisinvention is illustrated, a tire 10 is shown mounted on a wheel 12 forrotation about an axis 15. The tire 10 comprises an annular body 16 ofresilient elastomeric material having an outer cylindrical member 18 atthe outer periphery thereof on which a tread 20 may be mounted. Theannular body 16 is also provided with an inner cylindrical member 22 atits inner periphery which is adhered to or otherwise fastened to anouter cylindrical surface 24 of wheel rim member 12. Inner cylindricalmember 22 is of the same length as, coaxial to, and coextensive withouter cylindrical member 18.

The outer cylindrical member 18 is supported and cushioned by aplurality of circumferentially spaced-apart rib members 26, each ofwhich includes a first axial portion 28 (FIG. 3) and a second axialportion 30, and by a web member 32, which in this embodiment of theinvention is planar and is connected on one of its side faces 32a to thefirst portion 28 of rib members 26 and is connected on its other sideface 32b to the second portion 30 of rib members 26.

The planar web member 32 is positioned midway between the axial ends ofthe inner and outer cylindrical members 18 and 22. It is connected atits inner periphery 32c to the inner cylindrical member 22 and isconnected at its outer periphery 32d to the outer cylindrical member 18.Similarly, the various rib members 26 (FIG. 2) are connected at theirradially inner ends to the inner cylindrical member 22 and at theirradially outer ends to the outer cylindrical member 18. The ribs 26 arepreferably undercut where their ends connect to the inner and outercylindrical members, as shown at 34, to enhance flexibility of theconnection.

The rib members 26 extend generally axially along the inner and outercylindrical members 22 and 18 (Fig. 3) and, in the preferred embodimentas shown in FIG. 1 are inclined at an angle A (FIG. 1) of 15° to 75° toradial planes R which intersect them at their functions with the innercylindrical member 22. In an alternate embodiment (not shown), the ribmembers 26 can be extended radially with no angle A or with a lesserangle of between 0° and 15° . The web member 32 (FIG. 3) in thisembodiment lies in a plane that is perpendicular to the rotational axis14 of the tire 10.

In the preferred embodiment shown in FIGS. 1 to 3, the first axial ribmember portions 28 and the second axial rib member portions 30 are eachinclined at the same angle to the radial planes R which intersect themat their radially inner ends but the angles of the first portions 28 arepreferably oppositely directed with respect to the radial planes R fromthe angles of the second portions 30. Thus, as viewed in FIG. 3, thefirst rib portion proceeds upwardly from the section lines to connectwith the outer cylindrical member 18, while the second rib portion 30proceeds downwardly from the section lines to connect with the innercylindrical member 22.

In FIGS. 1-3, "r_(o) " is the outer radius of the annular body 16, "A"is the inclination angle that the rib members 26 make with the radialplanes R, "d_(i) " is the radial thickness of the inner cylindricalmember 22, "d_(o) " is the radial thickness of the outer cylindricalmember 18, "L" is the angularly directed length of the rib members 26,"D" is the radial distance from the outer surface of the innercylindrical member 22 to the inner surface of the outer cylindricalmember 18, "d_(w) " is the axial thickness of the web member 32, "d_(s)" is the thickness of the rib member 26 measured perpendicularly to itslength L, "t_(i) " is the axial length of the inner cylindrical member22, "t_(o) " is the axial length of the outer cylindrical member 28, and"t_(i) " is the radial dimension of the inner surface of the innercylindrical member 22.

In a tire of the type shown in FIGS. 1-3, the rib members 26 areconstrained to deform primarily in compression by the influence of theweb member 32, which may be cast as an integral part of the structure.The web member 32 tends to prevent the rib members 26 from deforming inbending, and the effect is to greatly increase structural stiffness. Inaddition, the rib members 26 tend to prevent the web member 32 frombuckling in the axial direction so the rib members and web member worktogether synergistically to carry tire loads.

Another desirable characteristic of a non-pneumatic tire or any tire isan overall spring rate that changes depending on the type of surfaceagainst which the tire is loaded. Specifically, it is desirable that thespring rate be lower over a bump or cleat than over a flat surface.

The annular body 16 may be adhered to the surface 24 of wheel rim 12 bybeing molded directly thereto in a liquid injection molding process,with the outer cylindrical surface 24 of the rim having been prepared inaccordance with known processes to adheringly receive the elastomericmaterial of the body 16. Preferably, the wheel rim 12 is provided withradial flanges 36 and 38 which cooperate with the mold in forming theannular body 16 on the wheel rim surface 24.

Method of Manufacture

The tire can be conveniently made in a mold having an inner cavity ofcomplementary shape to the tire 10 shown in FIGS. 1-3. The mold may havean inner mold ring substituted in place of the wheel rim 12. The mold isfilled with a reaction mixture of the preferred components of theinvention.

The reaction mixture is added to the mold under sufficient pressure toinsure that all air in the mold is displaced by liquid reaction mixture.It has been found that pressure in the area of 450 kPa is a suitablepressure. Once the mold is filled it is heated for about one hour forthe purpose of curing the liquid reactants. Subsequently, the mold isopened and the annular body 16 is demolded and post-cured for a suitablenumber of hours.

A simple tire tread composed of tough abrasion-resistant elastomer suchas conventional tire treads are manufactured from is applied to theouter cylindrical member 18. The tread has a minimal thickness to assurelittle heat build-up during flexing. A thickness of about 0.6 cm hasbeen found suitable. The tread may be adhered by conventional andwell-known adhesives which vary depending on the composition of thetread. If an inner mold ring has been substituted for the wheel rim 12,the rim 12 must be adhered by suitable adhesives to the inner surface ofthe annular body 16. The resulting assembly can be used to replace aconventional passenger car tire and wheel assembly. A car with the tireand wheel assembly can be driven without deleteriously affecting controlof the car without damage to the non-pneumatic tire of the invention.

Urethane Elastomer of the Invention

The invention resides in the specific selection of a polyether polyolprepolymer for the urethane elastomer which has at least two distinctmolecular weight polyols included in the prepolymer system.

The polyether used in this invention is the polyether having a terminalfunctional group containing active hydrogen capable of reacting with anisocyanate group. The functional group is selected from the groupconsisting of hydroxyl group, mercapto group, amino group and carboxylgroup.

Moreover, a pre-extended polymer obtained by reaction between a lowmolecular weight polymer and a diisocyanate or a product obtained byreaction between prepolymer and diol compound may be used in thisinvention.

Polyethers used in this invention are alkylene glycol such aspolyethylene glycol, polypropylene glycol, polytetramethylene etherglycol and the like, polyalkylene triol such as polypropylene triol andthe like, polyalkylene dicarboxylic acid, polyalkylene dithiol,polyalkylene diamine and their pre-extended polymer, and preferablypolyalkylene glycol, and more preferably polytetramethylene ether glycoland its pre-extended polymer.

In this invention, a mixture of two or more different kinds ofpolyethers having molecular weights which are different from each othermust be used. In this case, it is essential that at least one peak islocated at the lower molecular weight region (200-1,500) and at leastone peak is located at the higher molecular weight region (1,500-4,000).

Polytetramethylene ether glycol (PTMEG) is the most preferred polyol ofthe invention. A first low molecular weight polyether glycol is utilizedhaving a molecular weight of between 200 and 1,500. The essential secondhigher molecular weight polyether glycol has a molecular weight between1,500 and 4,000. A more preferred range for the low molecular weightmaterial is between 250 and slightly above 1,000. For the highermolecular weight second glycol, it is just below 2,000 to about 3,000.The most preferred range is is a low molecular weight glycol of about1,000 molecular weight and a higher molecular weight glycol of about2,000. The first and second polyether polyols may be blended in molarratios of between 95:5 to 50:50 where the first number in the ratio isalways the low molecular weight polyol. More preferred range is 90:10 to60:40. The most preferred range is 85:15 to 80:20.

The prepolymer for use in the tire of the invention is formed byreacting the first and second polyether polyols set forth above with amultifunctional isocyanate. The more preferred are the toluenediisocyanates. The two most preferred materials are 100% 2,4 toluenediisocyanate and the 80/20 blend of the 2,4 and 2,6 toluene diisocyanateisomers. The ratio of TDI to polyol is commonly expressed in the art asNCO:OH ratio. The isocyanate to polyol ratio may be in the range of1.7:1.0 to 2.3:1.0. A more preferred range of ratios is 1.85:1.0 to2.2:1.0. The most preferred range of ratios is 1.95:1.0 to 2.15:1.0. Thepercentage of free NCO in the resulting prepolymer is also in common usefor characterizing prepolymers.

Polyfunctional isocyanates used in this invention are not particularlylimited, but are preferably aromatic and aliphatic diisocyanates andtriisocyanates. Aromatic diisocyanates are, for example:

tolylene-2,4-diisocyanate;

tolylene-2,6-diisocyanate;

naphthalene-1,5-diisocyanate;

diphenyl-4,4'-diisocyanate:

diphenylmethane-4,4'-diisocyanate;

dibenzyl-4,4'-diisocyanate:

stilbene-4,4'-diisocyanate:

benzophenone-4,4'-diisocyanate;

and their derivatives substituted with alkyl alkoxy, halogen or nitrogroups, e.g., 3,3'-dimethylphenyl-4,4'diisocyanate or3,3'-dichlorodiphenylmethane diisocyanate, their mixtures and the like,aliphatic diisocyanates, and tricyanates. Among them, there may bepreferably used:

tolylene-2,4-diisocyanate;

tolylene-2,6-diisocyanate;

naphthalene-1,5-diisocyanate;

diphenyl-4,4'-diisocyanate;

diphenylmethane-4,4'-diisocyanate;

1,6-hexamethylene diisocyanate;

1,3 and 1,4-cyclohexyl diisocyanate;

methylene bis(4-cyclohexyl diisocyanate);

1,3- and 1,4-xylene diisocyanate and their mixtures.

The curing agents in this invention may be aromatic or aliphaticpolyamines or polyols. Aromatic diamines are, for example, 4,4'methylenebis(2-chloroaniline), 2,2',5-trichloro-4,4'-methylenediamines,napthalene-1,5-diamine, ortho, meta, paraphenylenediamine,tolylene-2,4-diamine, dichlorobenzidine, diphenylether-4,4'-diamine,their derivatives and mixtures.

Among them there are preferably employed 4,4'methylene bis2-chloroaniline, methylene dianiline, trimethyl bis(p-amino benzoate),bis amino phenylthioethane, napthalene-1,5-diamine, dichlorobenzidine,diphenylether, 4,4'-diamine, hydrazine, ethylenediamine,hexamethylene-1,6-diamine, piperazine, ethylene glycol, 1,3-propyleneglycol, 1,3 and 1,4-butane diol, trimethylpropane and their mixtures.

The final urethane elastomer is cured using aromatic organic diamineswhich are well-known and commercially available. The more preferredmaterial is 4,4'-methylene bis(2-chloroaniline) which will periodicallybe referred to as MBOCA. Also preferred is the diethyl toluene diamine(DETDA) which is available commercially from Ethyl Corporation under thetrade name Ethacure 100. A suitable material which has a different curerate is methylenedianiline-NaCl complex, commercially available fromUniroyal Chemical Company, Inc. as Caytur. The most preferred curativeis 4,4'-methylene bis(2-chloroaniline).

The stoichiometry of the prepolymer to curative is expressed on a molarequivalence basis, hereinafter called equivalence ratio, rather than ona weight basis. The broadest equivalence ratio of prepolymer to curativeis about 80 to about 115. More preferred is 90 to 110 and most preferredis 100 to 105. The equivalence ratio is also commonly called--percent oftheory--or simply stoichiometry.

It has been found through a long process of experimentation that severaldynamic properties of elastomers must be carefully evaluated together inorder to produce an elastomer suitable for the annular elastomeric bodyof the tire of this invention. A measure of dynamic modulus must revealthat the chosen elastomeric material has a relatively constant dynamicmodulus over a wide temperature range. The tendency of the elastomer tobuild up internal heat due to elastic inefficiency is commonly calledhysteresis in the industry. The hysteresis is commonly expressed interms of a value obtained from a hysteresis-type test which is commonlydescribed as tangent delta or, more commonly, tan δ. The tan δ shouldshow a decrease with a rise in temperature, indicating little internalheat build-up is occurring in the elastomeric body of article beingtested.

The flex fatigue test helps measure the ability of the elastomer towithstand the millions of cycles to which a non-pneumatic tire may besubjected. The test which has been found to correlate favorably withactual test tires is the cut growth resistance as run in accordance withASTM D-3629-78. Test conditions are: temperature 70° C., atmosphere isair, rate of rotation is 500 rpm and elongation is 23% . The deviceutilized is the TEXUS® Flex tester available from Testing Machines,Inc., New York, Model No. 31-11.

Dynamic measurements to determine a tan δ value are useful to assurethat a suitably low hysteresis value is obtained for the material.Several hysteresis devices are useful including the Rheovibran Tester,Hysterometer, and the Rheometrics Viscoelastic Tester for Solids, ModelRVE-S, made by Rheometrics, Inc., New Jersey. These instruments impose asinusoidal shear strain to the specimen, and analyze the torqueresponses and phase relation to the strain.

The ultimate test of the suitability of an elastomer for use in a highspeed tire is its ability to resist heat build-up and degradation atprolonged high speed service. United States Department of Transportationhas developed a test designated MVSS 109 high speed test procedure S5.5in which the test wheel and tire is run on a dynamometer at carefullyprescribed strain loads, dynamometer speeds and time periods. This testis designed for a pneumatic tire. The following is a simplifiedindication of the test regimen, specific details can be obtained byreview of MVSS 109. Load (NPS) 92% of maximum rated load in a 40° C.elevated temperature environment. Table I shows the speed intervals atwhich the tires described in the examples were run. The MVSS 109 testreviewed call for test termination after 31/2 hours (top speed 85 mph).However, in order to induce failure in the test tires, the test wascontinued as noted in Table I with incremental speed increases until thetires failed.

                  TABLE I                                                         ______________________________________                                        MVSS 109 Test Method                                                                   MVSS 109 Test Conditions                                                      Speed    Internal Cummulative                                                 (MPH)    (Hours)  (Hours)                                            ______________________________________                                        Load (NPS) 50         2        2                                              0.92 max load                                                                            75         1/2      21/2                                                      80         1/2      3                                                         85         1/2       31/2*                                                    90         1/2      4                                                         95         1/2      41/2                                                      100        1/2      5                                                         105        1/2      51/2                                                      110        1/2      6                                                         115        1/2      61/2                                                      120        1/2      7                                                          125**     1/2      71/2                                           ______________________________________                                         *MVSS 109 is stopped after 31/2hours @ 85 mph.                                **125 mph maintained for any additional time periods.                    

In order to determine the ultimate capability of a tire to withstandhighway conditions, this test was run beyond its normal termination timeof 31/2 hours to distinguish between materials used in the manufactureof the tire. Therefore, the life of the tire in hours may exceed the31/2 hour test specified in the Test Method.

SAMPLE AND TIRE PREPARATION PROCEDURE Comparative A-C and Examples 1,2

The polyether urethane compositions of Comparative A, B, and C., wereprepared by reacting a polytetramethylene ether glycol (nominal numberaverage molecular weight of 1,000) with toluene diisocyanate in ratiossufficient to produce a prepolymer having the NCO/OH ratio shown inTable II.

The prepolymers were then reacted with the designated diamine curativein the indicated ratios. It is conventional and well-known that thecurative and prepolymer may have to be preheated to facilitate handlingof the materials. If a small sample is being prepared for physicaltesting, the mixing is done batchwise in appropriate quantities. If thetire of FIGS. 1-3 is being produced, the curative and prepolymer arepumped continuously into a mixing head which injects the reactionmixture into a mold as earlier described under the subsection Methods ofManufacture.

Example 1 of the invention was prepared by sequentially reacting eachpolytetramethylene ether glycol with sufficient quantities of 80/202,4/2,6 TDI to form two distinct prepolymers which were then mixed inthe indicated molar ratio with the MBOCA curative as previouslydescribed.

Example 2 illustrates the most preferred method of manufacturing thetire of the invention. The 1,000 and 2,000 molecular weight PTMEGpolyols are preblended prior to forming the prepolymer with TDI. Theprepolymer is then reacted with the MBOCA curative to form the tire.This preblending of the polyols produces optimal properties in the tireas measured by TEXUS®Flex as shown in Table II under Test Results.

                                      TABLE II                                    __________________________________________________________________________                                Examples                                                                      1      2                                                       Comparatives   Blended                                                                              Preblended                                              A    B    C    Prepolymers                                                                          PTMEG                                      __________________________________________________________________________    Prepolymer Composition                                                        PTMEG         100  100  100  85     85                                        (1000 molecular wt.)                                                          PTMEG                        15     15                                        (2000 molecular wt.)                                                          2,4 toluene diisocyanate                                                                   X         X                                                      2,4-2,6 toluene diiso-                                                                          X         X      X                                          cyanate (80/20 blend)                                                         NCO/OH Ratio 2:1  2:1  2:1  2.15:1 2.15:1                                     % NCO        5.0  6.3  6.3  6.3    6.3                                        Curative                                                                      4,4-methylene bis(2-                                                                       X    X    X    X      X                                          chloroaniline)                                                                Equivalence Ratio                                                                           100  100  100  100    100                                       Physical Properties                                                           Hardness (Shore A                                                                           92   96   95   95     95                                        durometer)                                                                    Tensile, psi 5800 4700 6500 4730   4600                                       Elongation, %                                                                               420  410  380  390    410                                       Modulus, psi                                                                  100%         1400 1640 1800 1810   1730                                       200%         --   2070 --   2260   2120                                       300%         2600 --   4300 3130   2750                                       *Dynamic Properties                                                           Flex fatigue, cycles                                                                       3200 5000 2750 11250  13500                                      (TEXUS  ® Flex 70° C. @                                            23% elongation)                                                               Tire Life, Hours                                                                           2.0   4.25                                                                               3.28                                                                               5.50  --                                         (MVSS 109 - mph                                                                            (50 mph)                                                                           (90 mph)                                                                           (80 mph)                                                                           (105 mph)                                                                            --                                         at failure)                                                                   __________________________________________________________________________     *Dynamic properties values are average of following number of samples:        A--average of 3; B--average of 2; C average of 5; Example 1--average of 2     Example 2--single value.                                                 

The dynamic properties of Examples 1 and 2 illustrate the dramaticadvancement achieved by using blended PTMEG prepolymers of differentmolecular weight to produce the non-pneumatic tire of FIGS. 1-3. Theflex fatigue life of Example 1 is 135% better than the best of theComparative Examples-(B). The life of the tire of Example 1 isdramatically better, both in duration and the ultimate speedcapabilities. Example 1 lasted for 5.5 hours with the tire achieving aspeed of 105 mph in the final 30 minutes, as shown in Table I. Bycontrast, the best of the Comparative (B) failed at 4.25 hours at 90mph. U.S. Pat. Nos. 3,798,200 and 3,963,681 to Kaneko utilized similarpolyether urethane chemistry to yield the conclusion that the averagemolecular weight of a mixture of polyethers must fall in the range of4,500 to 20,000 average molecular weight or 1,000 to 4,500 with therequirement that the molecular weight of one polyether be less than4,500 and another must be above 4,500. The specific molecular weightranges were selected based on cut growth and flex crack resistance asmeasured according to De Mattia fatigue tester. Surprisingly, ourinvention relates to an appreciation that excellent tensile strengthand, more importantly, superior high speed tire performance in actualroad condition results from utilizing two distinct molecular weightpolyethers in the ranges of 200 to 1,500 and 1,500 to 4,000. ComparativeExamples 9 and 10 in U.S. Pat. No. 3,798,200 indicates that cut growthand flex crack resistance is poor using the De Mattia flex results.Therefore, this prior art reference teaches specifically away from theapplicant's invention in which it has been appreciated that acombination of physical properties relate most favorably and arepositively correlated with superior tire performance on both thedynamometer-type test as set out in MVSS 109 and in actual road courses.The average molecular weight should lie between 1,000 and 2,000 which iscontrary to the teachings and conclusions of U.S. Pat. No. 3,798,200 and3,963,681.

This invention resides in the recognition of the superior performanceprovided by a tire of the physical characteristics previously described(ribs and web structure) in conjunction with this specific polyetherurethane chemistry. This combination yields a tire which isnon-pneumatic in character but which can perform on the highway withdurability and vehicle handling characteristics similar to a pneumatictire.

It will be readily apparent to the skilled practitioner in the art thatmany modifications and changes can be made to the embodimentsspecifically documented herein. Such modification and changes are a partof the invention if they fall within the scope of the invention definedin the appended claims hereto.

What is claimed is:
 1. A method of manufacturing a non-pneumatic tirehaving improved hysteresis and flex fatigue resistance comprising thesteps of:(a) intimately preblending about 95 to 50 mol percent of afirst low molecular weight polytetramethylene ether glycol having amolecular weight of between 200 and 1,500 with about 5 to 50 mol percentof a second higher molecular weight polytetramethylene glycol having amolecular weight of between 1,500 and 4,000 to form a PTMEG blend: (b)reacting said PTMEG blend with toluene diisocyanate to form a mixedmolecular weight diisocyanate end capped polyether glycol prepolymer;(c) reacting said mixed molecular weight isocyanate end cappedprepolymer with an aromatic diamine curative in a mold having aninternal cavity shaped to form an annular body having a generallycylindrical outer member at the outer periphery thereof, a generallycylindrical inner member spaced radially inward from and coaxial withsaid outer member, a plurality of axially extending, circumferentiallyspaced-apart rib members connected at their corresponding inner andouter ends to said inner and outer cylindrical members, said rib membersbeing generally inclined at an angle of about 0° to 75° to radial planeswhich intersect them at their inner ends, and at least one web memberhaving opposite side faces, said web member having its inner and outerperipheries connected respectively to said inner and outer cylindricalmembers, said web member being connected on at least one of its sidefaces to at least one of said rib members to thereby form with said ribmember a load-carrying structure for said outer cylindrical member, saidload carrying structure being constructed to permit locally loadedmembers to buckle; and (d) demolding said annular body.
 2. A method ofmanufacturing according to claim 1 further comprising the step ofpreheating said mold prior to reacting said mixed molecular weightprepolymer with an aromatic diamine curative.
 3. A method ofmanufacturing according to claim 2 further comprising post-curing saidannular body at elevated temperature after said demolding step.
 4. Amethod of manufacturing according to claim 1 wherein said aromaticdiamine curative utilized in step (c) is 4,4'-methylenebis(2-chloroaniline).
 5. A method of manufacturing according to claim 1wherein said toluene diisocyanate is a 80/20 mixture of 2,4 toluenediisocyanate and 2,6 toluene diisocyanate.
 6. A method of manufacturingaccording to claim 1 wherein said first polytetramethylene ether glycolhas a molecular weight of about 1,000 and said second polytetramethyleneether glycol has a molecular weight of about 2,000 blended in a ratio ofabout 90:10 to about 60:40.